1. Field of the Invention
The present invention relates to a plasma ignition system used for ignition of an internal combustion engine.
2. Description of the Related Art
In a plasma ignition system for an internal combustion engine that ejects a plasma jet into a compressed air-fuel mixture, a large amount of ignition energy can be provided to the compressed air-fuel mixture and ignition performance can be improved, however, in the case where the charged voltage of a PJ (plasma jet) capacitor is extremely small or the like, so-called “failed plasma” may occur in such a way that spark discharge of the ignition plug occurs, but the subsequent plasma discharge does not occur. Further, if the charged voltage of the PJ capacitor is made larger, the failed plasma can be suppressed, but the inconvenience that the current flowing in the ignition plug at plasma discharge becomes larger and the plug life becomes shorter may be caused. As means for sparing the inconvenience, as shown in JP-A-2009-257112, after the start of plasma discharge using spark discharge of the ignition plug as a trigger, the charged voltage of the PJ capacitor may be switched from the high voltage to the low voltage.
The above described plasma ignition system erroneously ejects a plasma jet and causes damage on the internal combustion engine when the ignition plug is erroneously ignited due to external fluctuations because the charged voltage of the PJ capacitor is a higher set voltage as an absolute value relative to the discharge voltage of the ignition coil both at the high voltage and the low voltage. Further, when pressure within the combustion chamber of the internal combustion engine becomes negative, there are problems that the required voltage of the ignition plug becomes lower and the erroneous ignition is caused by the charged voltage of the PJ capacitor.